In recent years, with improvement of wireless communication networks including mobile telephone networks, service has become widespread that provides content to a terminal apparatus which is mounted and used on a mobile unit such as a car. It is preferable that the content to provide to the terminal apparatus mounted on a mobile unit is content related to positions through which the mobile unit passes.
The mobile unit and a provision source (for example, content server) of data (content data) that expresses the content are connected by communication paths including a wireless communication path. Data transmission rate is lower in the wireless communication path than in a wired communication path. Therefore, it is required to provide appropriate content at proper timing corresponding to the position to the terminal apparatus mounted on the mobile unit whose position changes with time.
As a conventional technique for providing content related to positions through which a mobile unit passes to the terminal apparatus, for example, the technique as disclosed in the following document is known.
Document: Sato, et al. “A Caching Algorithm for Location-aware Information Disseminated through Broadcast Media”, Information Processing Society of Japan, Vol.41, No.9, pages 2434 to 2444, September, 2000.
The conventional technique as disclosed in the document has a premise that a car (mobile unit) mounted with the terminal apparatus moves along a beforehand planned path. Then, the mobile unit acquires content data that expresses content via broadcast before presenting the information (content) related to a position on the moving path to a user, and stores the data in a cache of the terminal apparatus. Thus, it is intended to present the content at proper timing while apparently eliminating a waiting time for a user to access.
As described above, the conventional technique as disclosed in the document has the premise that the mobile unit mounted with the terminal apparatus moves along the beforehand planed path (scheduled path). Hence, the mobile unit acquires in advance content data that expresses the content related to a position near the scheduled path.
Therefore, according to the conventional technique, when the scheduled path is not set, the mobile unit cannot acquire the content data in advance.
Then, it is considered predicting a path of a mobile unit based on a current position of the mobile unit, and acquiring in advance content data that expresses the content related to a position near the predicted path. However, in this case, the mobile unit may move out of the predicted path. Therefore, the mobile unit has to acquire content data of wide range in advance. Accordingly, the mobile unit needs to store a number of items of content data that are not presented eventually, and as a result, cannot use the storage capacity of the terminal apparatus efficiently.
Further, in the above-mentioned document, a case is not considered where the time is long which is required for transmission from a content providing source to a terminal apparatus because the size is large of the content data that expresses the content. As in this case, when the time required for transmission of the content data is long, there is a possibility that the mobile unit has already passed through a position in relation to the content at the time transmission of the content data has been completed. In this case, it is not possible to present the acquired content data at appropriate timing, and the acquired content data becomes waste. As a result, the usage efficiency of the transmission path deteriorates.